1. Field of the Invention
The present invention is directed to a broad band controlled angle analog diffuser and associated methods. In particular, the present invention is directed to a diffuser which has the benefits of the wavelength independence of a refractive element and the design control of a diffractive element.
2. Description of Related Art
A binary or diffractive diffuser functions well as its design wavelength, but suffers significant contributions from the zero-order as the wavelength deviates from the design wavelength. The zero-order contributions arise from that light which is not diffracted. This will lead to undesirable peaks in intensity when the design wavelength is deviated from.
An attempt to compensate for this high sensitivity to wavelength variations is disclosed in commonly assigned, co-pending U.S. application Ser. No. 09/071,762 entitled xe2x80x9cBroad Band Diffractive Diffuserxe2x80x9d filed on May 5, 1998, the entire contents of which are hereby incorporated by reference. While such a diffuser allows some variation from the design wavelength, e.g., xc2x120%, the diffuser is still not wavelength independent. Further, while the broad band diffractive diffuser reduces zero order contributions at wavelengths other than the design wavelength, the divergence angles of the different wavelengths vary.
The wavelength dependence is inherent in the diffractive structure having etch depths related to the design wavelength xcex0, typically a xcex0/2(nxe2x88x921) etch depth for narrow band diffractive diffusers and typically a xcex0/(nxe2x88x921) etch depth for the broad band diffractive diffuser, where n is the refractive index of the material in which the structure is formed. However, diffractive diffusers have an advantage in that they allow the angle into which an incoming beam is diffused to be very precisely controlled.
In contrast, conventional refractive diffusers, such as a fly""s eye lens array, are relatively wavelength insensitive. However, the angular distribution over which these refractive diffusers radiate cannot be accurately controlled. For many applications, it is desirable to control this angular distribution. Typically when using refractive diffusers, this control is partially provided by the shape of the individual lenses or by an aperture to block angles other than the desired angles. The use of apertures results in an undesired loss in power. Creating lenses that are not spherical is typically very expensive, restricting the practical application of control of the angular distribution using the shape of the lenses. Finally, the use of two elements requires more space, which is often a significant constraint for the overall system in which the diffuser is incorporated.
The present invention is therefore directed to a broad band diffuser and method which substantially overcomes one or more of the problems due to the limitations and disadvantages of the related art.
These and other objects may be realized by providing an analog diffusing system for converting an input beam into an output beam having a preselected spatial energy distribution at an output plane including a computer generated structure having a plurality of regions, each region including free form shaped analog fringes, the input beam illuminating at least some of the regions, each region deflecting a majority of the portion of the input beam incident thereupon, so that at a target located at the output plane, the portion of the input beam deflected by several of the illuminated regions overlaps the portion deflected by at least one other illuminated region at the target to form the output beam. Preferably, the depth of a majority of the analog fringes is at least 2xcfx80 for wavelengths of interest.
These and other objects of the present invention may also be realized by an analog system for converting an incident beam into an output beam at an output plane spaced from the system, including a computer generated structure having a plurality of regions, each region having free form shaped analog fringes such that portions of the incident beam deflected by at least two regions of the plurality of regions overlap at the output plane, whereby the output beam has a preselected spatial energy distribution that is relatively insensitive to fluctuations in positioning of an input beam for incidence on the system, to spatial energy distributions within the incident beam, and to wavelengths of the incident beam.
The free form shaped analog fringes form a pattern which may be substantially discontinuous or substantially continuous at edges of the regions. The output beam may have a relatively uniform spatial energy magnitude and a preselected transverse beam shape. The depth of a majority of the analog fringes is preferably at least 2xcfx80 for wavelengths of interest.
These and other objects of the present invention may further be realized by an optical system including an analog diffusing element formed by a plurality of regions having a pattern thereon, the pattern being formed by smooth, free form shaped analog features, wherein each of the plurality of regions, when illuminated by a same input beam, transmits a beam with a predetermined angular spread, so that a given angular spread is imparted to the input beam, wherein the output beam is relatively insensitive to spatial energy distributions within the incident beam, and to wavelengths of the incident beam. Preferably, a majority of the analog features have a depth of at least 2xcfx80 for the wavelengths of interest
These and other objects of the present invention may also be realized by an analog optical element including a computer generated structure having a plurality of analog fringes, the analog fringes providing a statistical distribution of slopes in accordance with a desired output beam.
A majority of the analog fringes preferably have a depth of at least 2xcfx80 for wavelengths of interest, even more preferably, a depth of at least 20xcfx80 for wavelengths of interest. The desired output beam may have an angular distribution which is invariant across the output beam or which varies across the output beam. The cross-sections of the analog fringes may be curved, pyramidal, or sinusoidal. The fringes may be waves with a varying periodicity along perpendicular axes. The fringes may be formed in photoresist, which then may be transferred into a transparent substrate. The fringes may be formed on both sides of the element. The heights of the fringes may be the same, while the slope of the fringes is varied by altering a width of fringes. An intensity of light output by the analog optical element is preferably directly proportional to a surface area at a tangent normal for incident light.
These and other objects of the present invention may further be realized by a method of forming an analog optical element including forming analog fringes of a computer generated structure in an optically transparent material, the analog fringes having a statistical distribution of slopes in accordance with a desired output beam. The forming may include forming a majority of the analog fringes with a depth of at least 2xcfx80 for wavelengths of interest. Heights of the fringes may be varied to form the distribution of slopes. Widths of the fringes may be varied to form the distribution of slopes. The fringes may be formed in photoresist, and then may be further transferred into a transparent substrate. The forming may include creating a mask, placing the mask a distance from a photosensitive layer, exposing the photosensitive layer through the mask, and developing the exposed layer to create the fringes. The forming may include creating a gray mask, placing the mask on a photosensitive layer, exposing the photosensitive layer through the mask, and developing the exposed layer to create the fringes. The forming may include forming features on both sides of a substrate. The forming may include varying the statistical distribution of slopes across the optically transparent material. The forming may include maintaining the statistical distribution of slopes across the optically transparent material.
These and other objects of the present invention will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.